This invention relates to laminates, and more particularly to thin laminate structures intended for use as anti-friction and slide bearing members wherein a metallic substrate strip has bonded to it an anti-friction or slide layer of plastics material. The anti-friction slide layer can consist of thermally, highly-stressable plastics and can contain thermosetting polyimide resins and additives which improve the running properties of a bearing, such as polytetrafluorethylene, metallic bearing alloys or the like. The slide layer additionally can contain polyimide resins and other additives, as for example polyimide lacquer as a binding and bonding agent, and polyimide resins in fine-grained or fine-powdered form.
It is an object of the invention to improve the above, known laminates of this kind considerably, so that in addition to good low-friction and sliding characteristics there is had a much greater heat and abrasion resistance.
According to the invention, the fine-grained or fine-powdered polyimide resin mixture which the polyimide lacquer binds is supplemented with a highly heat and abrasion resistant thermoplastic material from the group consisting of polyarylene sulfide and/or aliphatic polysulfide and/or polysulfone, thereby to effect the above-identified improvements.
As found through actual tests, a surprisingly and unexpectedly great improvement of the heat and abrasion resistance of the anti-friction or slide layer is attained by the addition of one or more of such thermoplastic materials from the group mentioned.
The additive thermoplastic material, preferably polyphenylene sulfide, is incorporated as a fine-grained powder with the other additives that are used to improve the running properties. The percentage of such thermoplastic material which is added to improve the heat resistance and increase the abrasion resistance should be between 30 percent by weight up to 80 percent by weight, relative to the total weight of the anti-friction or slide layer, This means that the constituents depended on to improve the running properties of the bearing can be constituted completely of the thermoplastic additive substance provided by the invention for the purpose of improving the heat and abrasion resistance. We have also found that it is possible to admix the special additive thermoplastic material which improves the heat and abrasion resistance, to other additives which are especially adapted to improve the running properties of the slide layer, and that the minimum percentage of the additive which increases the abrasion resistance should be near 30 percent by weight, relative to the total weight of the anti-friction or slide layer. Materials which are suitable for use as additives, to be admixed with the additive thermoplastic material that improves the heat and abrasion resistance are: Finely powdered graphite, molybdenum disulfide and oxides. There can also be embedded in the slide layer, for instance, at the location of the bonding surface between the slide layer and the substrate, a supporting matrix such as of bearing material. This supporting matrix can be, for example, of stannous bronze, and can be in the form of a weave of strands or wires.
In another embodiment of the invention, the side surface of the substrate which supports the anti-friction or slide layer can be coated with a sinter skeleton, such as of bearing alloy.
But the substrate itself can also be constituted of a sinter skeleton, such as of bearing alloy. Other possibilities are that the substrate is constituted of perforated steel or bronze sheet.
The anti-friction or slide layer can be approximately 0.1 mm to 0.5 mm thick and can be machined by chip making methods on its running surface, if applicable.
For the production of the laminate according to the invention, a method can be employed in which a band constituting the substrate is coated continuously with the material that forms the anti-friction or slide layer, as by intimately mixing the ingredients of this material, namely polyimide lacquer, finely powdered polyimide resin, and fillers, and thereafter homogenizing them to a high-viscous or pasty form, after which the mixture so prepared is applied to the substrate in a quantity corresponding to the desired coating thickness. The coated mixture is then hardened on the substrate.
According to the invention, the laminate as provided herein can be advantageously produced by a better method, as well, which is characterized in that the ingredients of the material forming the anti-friction or slide layer, namely polyimide lacquer, fine-grained or fine-powdered polyimide resin, and filler, are mixed intimately, homogenized to a high-viscous or pasty form, and then, after incorporating the thermoplastic additive materials, the viscoity as thus increased is altered to a lower value suited for the electrostatic spray of the mixture, whereby the anti-friction or slide layer can be continuously applied to a band constituting the substrate by an elctrostatic spraying method, and then subsequently hardened.
The advantage of this latter method is that an extremely uniform coating is assured, which makes an aftertreatment unnecessary or, if required, necessary only to a slight degree. In the method according to the invention, the coated band can be worked to the specified final thickness by rolling it, prior to the final hardening process.